This invention relates to wrapping materials for light-sensitive materials, and particularly to wrapping materials for light-sensitive materials which satisfy various characteristics desired for wrapping materials, such as physical strength, light-shielding properties, moisture resistance, antistatic properties and heat-shielding properties, etc., and which can be produced economically.
In general, wrapping materials which completely shield light are used for wrapping light-sensitive materials such as photographic films or printing paper, etc., because the light-sensitive materials lose their qualities and value if exposed to light. When using such wrapping materials as packaging bags, it is necessary that they have sufficient physical strength, namely, breaking strength, tear strength, bursting strength, surface strength and bag breaking strength, etc., depending on the size and weight of object to be packaged. Furthermore, in the case of packaging light-sensitive materials in bags of such wrapping materials, it is necessary that the wrapping materials have a heat-sealing property and heat-sealing strength, in order to achieve light-shielding and moisture proofing by completely sealing the opening part thereof by heat-sealing. When the opening part of the package bags is sufficiently sealed by heat-sealing, the heat-sealed part substantially does not leak the light to the inside, but as further protection in practical embodiments, the heat-sealing part is folded two or three times. Moreover, it is necessary that the wrapping materials have an antistatic property, in order to prevent generation of electric charges caused by friction between the light-sensitive materials in the packaging bag and the wrapping material.
Hitherto, as wrapping materials as described above, compound laminates composed of a low density polyethylene film containing carbon black or pigment, and a paper, aluminum foil or cellophane, etc., have been known in general.
The following steps have been taken for these wrapping materials so as to satisfy the above-described characteristics.
(1) Light-shielding property: Carbon black is added. In the case of adding it in a particularly large amount (by which light-shielding can be attained with a thin layer), low density polyethylene, ethylene-acrylic acid ester copolymer and ethylene-vinyl acetate copolymer, etc., are used. PA1 (2) Moisture resistance: Low density polyethylene films having large moisture permeability and ethylene-acrylic acid ester copolymer or ethylene-vinyl acetate copolymer films can be used, but must be used as a relatively thick layer or laminated with an aluminium foil. However, high density polyethylene films can be utilized with only a slightly increased thickness, because the moisture permeability thereof is only about 1/3 that of the low density polyethylene films. PA1 (3) Physical strength: Polyethylene is laminated with paper in order to increase tearing strength, synthetic rubber is added to low density polyethylene, or the total thickness of the film is increased. PA1 (4) Antistatic property: Carbon black is added, by which it is obtained simultaneously with light-shielding. The same purpose can be attained by laminating with an aluminium foil, too.
However, such prior packaging bags have drawbacks in that they too often tear or break during the packaging operation, or are easily extended by pulling.
In order to overcome these drawbacks, it is necessary to increase the thickness of packaging bags, and consequently such packages may become bulky, heavy, and expensive.
On the other hand, several proposals concerning wrapping materials having the above-described characteristics and, particularly, improved physical strength have been done.
For example, Japanese Utility Model Registration Application (OPI) No. 133631/77 which corresponds to U.S. Pat. No. 4,147,291 discloses packaging bags for light-sensitive materials which comprise a cross laminate film consisting of two monoaxially stretched high density polyethylene films the drawing directions of which cross each other at an angle of from 45.degree. to 90.degree. and a low density polyethylene film bonded to said laminate film. Similarly, Japanese Utility Model Registration Application (OPI) No. 21168/80 which corresponds to U.S. Pat. No. 4,258,848 discloses wrapping materials for light-sensitive materials which comprise two or more high density polyethylene films drawn monoaxially within a prescribed drawing ratio, which are bonded with an adhesive layer such that the drawing axes thereof cross each other at an angle of from 45.degree. to 90.degree.. FIG. 1 and FIG. 2 each indicate a cross-sectional view which indicates a layer construction of wrapping material of the latter type. In the drawings, 1' is a monoaxially drawn high density polyethylene film containing a light-shielding agent, 2 is an adhesive layer and 4 is an aluminium foil.
Hitherto, materials prepared by knitting lengthwise and breadthwise high density polyethylene flat yarns each having a different drawing direction (as described. e.g., in U.S. Pat. Nos. 3,445,055 and 3,816,230), materials prepared by heat-sealing a network of thermoplastic films by means of an embossed roll (described, e.g., in U.S. Pat. No. 3,973,063), and materials prepared by bonding high density polyethylene films each having a different drawing direction through an intermediate layer (described, e.g., in U.S. Pat. No. 3,322,613), etc., have been known as wrapping materials for other than light-sensitive materials. However, such drawn high density polyethylene films have not been utilized as wrapping materials for light-sensitive materials. In this sense, the wrapping materials for light-sensitive materials as disclosed in Japanese Utility Model Registration Application (OPI) Nos. 133631/77 and 21168/80 are unique. When the above-described wrapping materials for light-sensitive materials are used, a further improvement can be obtained as compared with the prior wrapping materials for light-sensitive materials, because they are particularly excellent in physical strength, such as tearing strength or bursting strength, etc., and satisfy various characteristics, including the light-shielding property and heat-shielding property, and economic considerations.
However, when a wrapping material as indicated in FIG. 1 is used, moisture resistance is not always sufficient. Therefore, in case of packaging light-sensitive materials which require moisture resistance, wrapping materials comprising an aluminium foil 4 as shown in Table 2 have been necessarily used.
In this case, however, since it is necessary to provide adhesive layers 2 on both sides of the aluminium foil 4, the total thickness of the material is increased, the layer construction becomes complicated, and there is a disadvantage in that the cost increases as compared with a material as indicated in FIG. 1.